Project Summary: The overall goal of this research is to develop a three-dimensional (3D) and multispectral fiber-bundle endoscope for the real-time, non-invasive assessment of biological tissue. Optical endoscopy has been extensively employed worldwide by physicians to diagnose or treat diseases, such as cancer. These probes are inserted into the body through small incisions or natural body openings, providing high-resolution images of internal organs and tissue. Depending on whether the image is transmitted through lenses alone or fibers, optical endoscopes are generally classified into two categories, rigid and flexible. Compared with the rigid counterparts, flexible endoscopes feature a lower rate of complications, increased patient comfort, and a lack of requirement for general anesthesia. Moreover, they allow the visualization of the entire gastrointestinal tract, such as esophagus, stomach, and duodenum, which are generally inaccessible by rigid endoscopes. Despite widespread use, conventional flexible optical endoscopes have been crucially limited to 2D views of pathological sites. Because most tissue lesions manifest themselves as abnormal 3D structural changes, the lack of depth information frequently jeopardizes the diagnostic usefulness. On the other hand, the value of spectral imaging for phenotype description and as a quantitative assessment tool for tissue abnormalities has continued to grow exponentially. Nonetheless, to acquire the color information, most conventional spectral imagers rely on scanning, either in the spatial or spectral domain. Limited by the scanning mechanism, these imagers are generally slow in data acquisition and therefore unsuitable for imaging dynamics. To overcome above limitations, we propose flexible light field endoscopy (Flex-LFE) which will enable 3D and multispectral imaging of tissue lesions in real time. The Flex-LFE will be built upon a computational imaging architecture that has been previously demonstrated in photography. However, rather than imaging macroscopic objects, we will tailor Flex-LFE for flexible endoscopic imaging in two specific aims: i) develop a Flex-LFE for 3D and multispectral imaging of biological tissue, ii) evaluate the probe?s imaging performance both in phantoms and ex vivo. The proposed Flex-LFE will have broad impacts on the endoscopic diagnosis and treatment. The acquisition of 3D and spectral information will facilitate the identification of a variety of tissue lesions, alleviating the need for invasive tissue biopsy. Moreover, the probe?s fast 3D imaging capability will enable real-time monitoring of laparoscopic interventions, providing accurate 3D visualization of surgical sites and thereby reducing the risk of misidentifying structures, a situation that can cause severe patient injuries. As the first instrument of its kind, the development of Flex-LFE will ultimately lead to a new generation of optical 3D endoscopes and make transformative advancements to the state-of-the-art approaches.